This invention relates to electric motors and particularly to stepping motors which are magnetically enhanced to increase the effective torque produced by the motor.
Generally a stepping motor includes a rotor with outwardly-projecting peripherally-spaced longitudinally-extending rotor teeth which interact with inwardly-projecting peripherally-spaced longitudinally-extending stator teeth. The latter are mounted in sets on peripherally-spaced inwardly-projecting longitudinally-extending stator poles such that the stator teeth on one pole may align with the opposing rotor teeth while the teeth on the adjacent pole are partially misaligned with the rotor teeth, and the stator teeth on the next peripherally-spaced pole align with the valleys between opposing rotor teeth. In a so-called "hybrid" motor, the rotor contains two axially aligned sections with teeth of one section aligned with the valleys of the other section. A permanent magnet between the two rotor sections magnetizes the sections in opposite polarities. Appropriately energizing coils on the stator poles causes an interaction between the stator and rotor teeth that turns the rotor.
In some stepping motors, the pitches on the stator teeth differ from those on the rotor teeth. The aforementioned stepping motor principles of operation are also used on linear stepping motors where the rotor is replaced by a linear actuator.
The efficiencies and torques of such motors have recently been increased by inserting radially-poled permanent magnetic materials in the valleys between the stator teeth or the stator teeth and rotor teeth. Preferably, the materials used are high coercive force materials such as samarium cobalt or neodymium boron iron alloys which are formed into a powder, pressed, sintered and glued into the valleys. While materials such as ferrite can also be used, these are less effective. The preferred materials are generally expensive, difficult to handle, and require a number of manufacturing steps. They also add to the overall weight of the motor.